Let's see if I can answer your questions.
I own a 12 x12 and it is turning into an amazing little machine. Put together and tweaked in a 7 x 7 should be great, but with smaller machining range.
Thr repeatabiltiy on my machine is spot on. Just the other day I needed to make a bunch of semi complex widgets and the machine happily machined them all out in a single job.
Limit switches or sensors? I am using switches for my homing and they work fine. I am not using limit switches and haven't had any problems.
I am finding out that these machines can pretty much do any type of material. One just has to play around with feeds and what type of cutter to use. I am just getting ready to do some testing with aluminum. My shipment of new cutters just arrived so the experimenting will begin shortly.